Last week we conducted a webinar – "Breaking the Form Barrier – Evolution of LTE & Enterprise Femtocells" – that generated a lot of incisive questions about the implementation challenges and solutions for next generation femtocells. We received more questions than we were able to answer in the time we, so the Aricent experts that led the webinar, Sanjiv Kapur and Siddhartha Bhakta, have gone through the unanswered ones with responses below.
Q: How will CDMA be incorporated in next generation femtocells?
A: LTE and other next generation telecommunication technologies will need to co-exist with older technologies such as UMTS, CDMA and GERAN, etc. Deploying stand-alone solutions supporting individual technologies can be prohibitively expensive for both operators and subscribers.
Multi-mode femtocells - capable of supporting multiple technologies simultaneously - provide a solution for deploying these technologies to ensure that expenses are kept under control. These femtocells will provide support for LTE and one or more older technologies based on the operator’s requirements.
Q: How can interference be reduced when macrocells and femtocells need to use the same carrier?
A: Various standard bodies have laid down detailed specifications for deployments of small cell solutions that minimize interference between base stations of different form factors.
The amount of power delivered to each femtocell determines its coverage area. Femtocell deployments can be designed to eliminate coverage holes in the macro cell UE coverage area.
Q: Are there any standardization efforts on SON for LTE femtocells?
A: The standards for self optimizing networks (SON) are evolving and there is very little guidance available today on actual implementation. There is significant room for differentiation between vendors especially in case of small cell solutions such as femtocells.
Femto Forum is actively working on recommending the SON requirement for Femtocell. The 3GPP TR 36.921 and 3GPP TR 36.922 specifies standards for Self configuration of LTE Femtocell.
Q: X2 interface needs to be carried over an IPSec tunnel. In a mesh environment this would imply that femtocells would need to support as many IPSec tunnels as the neighboring eNodeB. Can the number of IPSec supported thus become a limiting factor for a femtocell in metro cell environment?
A: Typically in a mesh environment there is an aggregation node that terminates IPSec tunnels towards EPC and other eNodeB. Femtocells can have a single IPSec tunnel with aggregation node for S1 and X2 purposes. This aggregation will act as a bridge between two IPSec tunnels from two eNodeBs. So the number of IPSec tunnels ceases to be a limiting factor in deployment of femtocell solutions.
Q: How are femtocells powered in the field and in the home? What happens when there is a power outage?
A: Femtocells are powered using consumer’s power and use existing ADSL/Cable modem connection, thus eliminating the need for huge investments by operators.
In case of a power outage at a consumer’s site, the UE latches on to the macro cell and switches back to the femtocell once power is restored.
Q: Would LTE femtocell be marketed as operator subsidized?
A: Most likely! The operator today subsidizes most femtocell deployments. Operators are under huge pressure to reduce the cost per bit of providing data services and macro cells deployments are complex and expensive.
Femtocells provide huge benefits to operators, not just in terms of saving deployment and operational expenses, but also reducing the load on core macro networks via offloading. Subsidizing the cost of femtocell deployment also helps in improving customer loyalty, thus enhancing the overall user experience.
Q: What is the advantage of integrated GW into each femtocell?
A: There are primarily two advantages of incorporating Local Gateways (LGW):
- It enables IP capable UEs to access IP capable entities (e.g., home devices) in the same residential/enterprise IP network without the user plane traversing the mobile operator's network.
- It also enables IP capable UEs to access the Internet without going through the mobile operator's core network - reduceing the stress on the core network.
Q: What are the choices for backhaul? Which is preferred and why? How do you solve the backhaul challenge for wide spread deployment of femtocells?
- For Residential Femtocell, typically xDSL or Cable backhaul is used.
- For Enterprise Femtocell, the SONET or ATM backhaul (exists on Enterprise) is used.